US4495142A - Monitoring system for monitoring state of nuclear reactor core - Google Patents

Monitoring system for monitoring state of nuclear reactor core Download PDF

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Publication number
US4495142A
US4495142A US06/245,515 US24551581A US4495142A US 4495142 A US4495142 A US 4495142A US 24551581 A US24551581 A US 24551581A US 4495142 A US4495142 A US 4495142A
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Prior art keywords
radioactivity
level
measuring
outputs
iodine
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US06/245,515
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Tadakazu Nakayama
Ryozo Tsuruoka
Masaki Matsumoto
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Hitachi Ltd
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Hitachi Ltd
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Assigned to HITACHI, LTD. reassignment HITACHI, LTD. ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: MATSUMOTO MASAKI, NAKAYAMA TADAKAZU, TSURUOKA RYOZO
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    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C9/00—Emergency protection arrangements structurally associated with the reactor, e.g. safety valves provided with pressure equalisation devices
    • G21C9/004—Pressure suppression
    • G21C9/012—Pressure suppression by thermal accumulation or by steam condensation, e.g. ice condensers
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C17/00—Monitoring; Testing ; Maintaining
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E30/00—Energy generation of nuclear origin
    • Y02E30/30—Nuclear fission reactors

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  • the present invention relates to a system for monitoring the state of a nuclear reactor core and, more particularly, to a monitor system for monitoring the state or condition of a nuclear reactor core, employing a radiation monitor suitable for monitoring the state of a nuclear reactor core at the time of loss of coolant accident (referred to as LOCA, hereinafter).
  • LOCA loss of coolant accident
  • the boiling water reactor has a reactor containment vessel consisting of a dry well and a pressure suppression chamber.
  • the reactor pressure vessel is placed in the dry well, while the pressure suppression chamber is filled with cooling water.
  • the cooling water of high pressure and temperature in the pressure vessel is dischaged as steam into the dry well through the fractured portion of the primary loop recirculation system. This steam is introduced into the pressure suppression chamber and is condensed by the cooling water in the latter.
  • a radiation meter, thermometer, pressure gauge and a condensate drain level meter are installed in the dry well of the boiling water reactor, in order to monitor the leakage of the cooling water due to LOCA.
  • This monitoring system permits the operator to confirm occurrence of LOCA, but cannot provide accurate information concerning the state or condition of fuel rods in the reactor core after occurrence of LOCA. Therefore, with this known monitor system, it is not possible to take suitable countermeasures after the occurrence of the LOCA.
  • a monitoring system comprising: means for measuring a level of the radioactivity of iodine in the primary containment vessel of a nuclear reactor; means for measuring a level of the radioactivity of noble gas; and means for judging or determining the state or condition of fuel rods in the reactor core in the event of occurrence of LOCA, upon receipt of the output from the means for measuring the level of the radioactivity of iodine and the output from the means for measuring the level of the radioactivity of noble gas.
  • FIG. 1 is a system diagram of a monitoring system for monitoring the state of a nuclear reactor core constructed in accordance with an embodiment of the invention, applied to a boiling water reactor;
  • FIG. 2 shows the detail of an iodine monitor incorporated in the system shown in FIG. 1;
  • FIG. 3 shows the detail of a noble gas monitor incorporated in the system shown in FIG. 1;
  • FIG. 4 shows the detail of a liquid radiation monitor incorporated in the system shown in FIG. 1;
  • FIG. 5 is a flow chart of an accident judging device incorporated in the system shown in FIG. 1;
  • FIG. 6 shows the state of an image surface of a display device when there is a flow of coolant into the pressure suppression chamber due to an LOCA;
  • FIG. 7 shows the state of the image surface of the display device when there is a perforation of fuel rod in the event of the LOCA;
  • FIG. 8 shows the state of the image surface of the display device when there is a melt down of fuel rod in the event of the LOCA
  • FIGS. 9 and 10 are system diagrams of different embodiments applied to a boiling water reactor.
  • FIG. 11 is a system diagram of a different embodiment of the invention applied to a pressurized water reactor.
  • the present inventors have found that the occurrence of an LOCA can easily be recognized and the state of fuel rods after occurrence of the LOCA can be determined, through measurement of levels of radioactivities in iodine and noble gas in the primary containment vessel of the reactor, as will be understood from the following description.
  • An iodine monitor and a noble gas monitor which are adapted to measure a level of the radioactivity in the radioactive iodine and that of the radioactive noble gas in the pressure suppression chamber, respectively, are incorporated in the monitor system of the invention.
  • the system further has a liquid radiation monitor adapted for measuring a level of the radioactivity in the cooling water within the pressure suppression chamber.
  • the radioactivities measured by the iodine monitor, the noble gas monitor and the liquid radiation monitor are expressed by X, Y and Z ⁇ ci/cc, respectively.
  • (X+Y) shows the level of the total radioactivity in the gas layer within the pressure suppression chamber
  • (X+Y+Z) shows the level of the total radioactivity in the pressure suppression chamber.
  • the value (X+Z) represents the level of the total radioactivity of iodine in the gas and the liquid layers within the pressure suppression chamber, because the radioactivity in the liquid layer is carried almost fully by the iodine.
  • the value [Y/(X+Z)] shows the ratio of the radioactivity between the radioactive noble gas and the radioactive iodine.
  • (X+Y+Z) and [Y/(X+Z)] are useful in judging (a) normal operation of the nuclear reactor, (b) flow of cooling water into the pressure suppression chamber in the event of LOCA, (c) perforation of fuel in the event of LOCA and (d) melt down of fuel in the event of LOCA.
  • the level of the radioactivity of the cooling water in the pressure suppression chamber during normal operation of the nuclear reactor is about 10 -3 ⁇ ci/cc. Almost no radioactive noble gas exists in the pressure suppression chamber. Therefore, the following condition is met during the normal operation of the nuclear reactor.
  • the cooling water discharged in the state of steam from the pressure vessel into the dry well, in the event of an LOCA, is condensed into water upon contact with the cooling water pooled in the pressure suppression chamber.
  • the level of the radioactivity in the cooling water in the pressure suppression chamber is increased by at least one decimal place due to the flowing of the cooling water into the pressure suppression chamber. If there is no perforation of the fuel rods, there is almost no noble gas in the pressure suppression chamber. Therefore, in the event that the cooling water in the pressure vessel has been discharged into the pressure suppression chamber, the relationship represented by the following equations (2) is established.
  • the levels of the radioactivities of the radioactive noble gas and the radioactive iodine are 10 5 ⁇ ci/cc and 10 3 ⁇ ci/cc, respectively.
  • the level of radioactivity in the radioactive iodine in cooling water of the pressure suppression chamber is 10 4 ⁇ ci/cc. Therefore, the following relationships are established when all of the fuel are broken and have suffered a melt down in the event of LOCA.
  • the primary containment vessel 4 of the boiling water reactor consists of a dry well 5 and a pressure suppression chamber 6 both of which are closed vessels.
  • the pressure suppression chamber 6 is ring-shaped and is filled with cooling water.
  • a bent pipe 9 communicated with the dry well 5 is inserted into the pressure suppression chamber 6.
  • a downcomer pipe 10 is connected at its one end to the bent pipe, while the other end of the downcomer pipe 10 is immersed in the cooling water.
  • a gas layer 8 is formed on the surface of the cooling water 7 in the pressure suppression chamber 6.
  • a nuclear reactor pressure vessel 1 having a core 2 therein is disposed in the dry well 5.
  • a pipe 11 communicates at its both ends with the gas layer 8 in the pressure suppression chamber 6.
  • the pipe 11 is provided with a blower 12.
  • An iodine monitor 13 and a noble gas monitor 18 are installed in the pipe 11.
  • the constructions of the iodine monitor 13 and the noble gas monitor 18 will be described in detail hereinunder with specific reference to FIGS. 2 and 3.
  • the iodine monitor 13 has an iodine filter 15 disposed in a chamber 14 provided in the pipe 11.
  • a radiation detector 16 is disposed at the outside of the chamber 14.
  • the chamber 14 and the radiation detector 16 are surrounded by a radiation shielding body 17.
  • the noble gas monitor is constituted by a chamber 19 provided in the pipe 11 and a radiation detector 20 disposed in the chamber 21.
  • the chamber 19 and the radiation detector 20 are surrounded by a radiation shielding body 21.
  • a pipe 22 has both ends placed in the cooling water 7 in the pressure suppression chamber 6.
  • a pump 23 and a liquid radiation monitor 24 are provided in the pipe 22.
  • the liquid radiation monitor 24 has a construction as shown in FIG. 4.
  • a chamber 25 for receiving a radiation detector 26 are provided in the pipe 22.
  • a radiation shielding body 27 surrounds the chamber 25 and the radiation detector 26.
  • the monitoring system for monitoring the state of a reactor core in accordance with the present invention is constituted by an iodine monitor 13, a noble gas monitor 18, a liquid radiation monitor 24, an accident judging device 28 and a display device 29.
  • the monitoring system of the first embodiment having the construction described hereinbefore operates in a manner explained hereinunder. Since the blower 12 is driven continuously, the gas constituting the gas layer in the pressure suppression chamber is circulated through the pipe 11 so that levels of the radioactivities in the radioactive iodine gas and the radioactive noble gas in the circulated gas are measured by the radiation detectors 16 and 20 of the iodine monitor 13 and the noble gas monitor 18. The outputs from these detectors are then delivered to the accident judging device 28 which may be a computer. Since the pump 23 operates continuously, the cooling water 7 in the pressure suppression chamber 6 is continuously circulated in the pipe 22. The level of the radioactivity in the cooling water 7 is measured by the radiation detector 26 of the liquid radiation monitor 24, and is delivered to the accident judging device 28. The accident judging device 28 operates to judge the state of the reactor core in accordance with the flow chart shown in FIG. 5, the result of which is shown at the display device 29.
  • the accident judging device 28 receiving the outputs from the radiation detectors 16, 30 and 26 makes, at a step M1, a judgment concerning the condition of X+Y+Z ⁇ 10 -3 ⁇ ci/cc. In this case, since the levels of outputs from the detectors are low, the judging device 28 provides an answer YES. In this case, the display device 29 makes a display of "NO LOCA" in red.
  • the LOCA takes place when there is a rupture in the reactor pressure vessel 1 or in the recirculation pipe 3.
  • the cooling water of high-pressure and temperature in the pressure vessel 1 is discharged as steam of high temperature and pressure through the fractured portion to fill the dry well 5.
  • the steam is then introduced by the bent pipe 9 and the downcomer pipe 10 into the cooling water 7 in the pressure suppression chamber 6 so as to be cooled and condensed upon contact with the cooling water 7.
  • the cooling water in the pressure vessel is scattered away so that an emergency core cooling system (not shown) is started to spray cooling water into the pressure vessel 1.
  • the level of the radioactivity in the pressure suppression chamber 6 changes in a manner shown in FIG. 6, in the case where there is no fuel rod perforation in the reactor core 2 in the pressure vessel 1 of the nuclear reactor, in the event of an LOCA.
  • FIG. 6 shows the state of an image surface of the display device 29. More specifically, in FIG. 6, the full-line curve shows the output from the radiation detector 16 of the iodine monitor 13, i.e. the level of radioactivity in the radioactive iodine in the gas layer 8, while the one-dot-and-dash line curve in the same Figure shows the output from the radiation detector 20 of the noble gas monitor 18, i.e. the level of the radioactivity in the radioactive noble gas in the gas layer 8. Also, the broken-line curve shows the output of the radiation detector 26 of the liquid radiation monitor 24, i.e. the level of the radioactivity of radioactive iodine in the cooling water 7. As mentioned before, almost all of the radioactivity in the cooling water 7 is carried by radioactive iodine.
  • the steam of cooling water discharged from the pressure vessel 1 into the dry well 5 flows into the pressure suppression chamber 6 so that the level of the radioactivity in the cooling water 7 is abruptly increased as shown by broken line in FIG. 6 (Point a).
  • the liquid radiation monitor 24 indirectly measures the level of the radioactivity of the condensate liquid of the steam discharged into the dry well 5. Since the radioactive iodine in the cooling water 7 moves into the gas layer 8, the level of the radioactivity measured by the iodine monitor 13 increases as shown by the full-line curve. However, the output from the noble gas monitor (one-dot-and-dash line) does not increase substantially.
  • the accident judging device 28 makes a judgement at step M1 of FIG. 5 in accordance with the equations (2) mentioned before, using the outputs from respective radiation detectors, and provides a conclusion NO. Then, the judging device 28 makes a judgement at step M2 as to whether the condition of Y/(X+Z) ⁇ 10 -3 is met. In the case where there is no perforation of the fuel rod, the judging device 28 provides an answer YES as a result of judgement in the step M2. Therefore, the display device 29 makes a display of "LOCA OCCURRED" and "NO FUEL ROD PERFORATION" in red, as shown in FIG. 6. The fact that the condition of judgement at step M1 is not met means the occurrence of a LOCA.
  • FIG. 7 shows that a LOCA has taken place at the moment (a) and that a perforation of a fuel rod took place at a moment (b). If there is any perforation of a fuel rod in the reactor core 2, a large amount of radioactive noble gas is discharged from the broken fuel rods.
  • the accident judging device 28 provides an answer NO in each of the steps of M1 and M2 of the judgement.
  • the accident judging device 28 then makes a judgement at a step M3 as to whether the condition of Y/(X+Z) ⁇ 9 is met, and provides an answer YES.
  • the accident judging device 28 then makes a judgement as to whether the condition of X+Y+Z ⁇ 10 -2 ⁇ ci/cc is met at a step M4.
  • An answer NO is obtained as a result of judgement in this step so that the display device 29 makes a display of "LOCA OCCURRED” and "FUEL ROD PERFORATION” in red. If the perforation of the fuel rod is not spreading, the amount o2f radioactive substance discharged from the fuel rod is not spreading, the amount of radioactive substance discharged from the fuel rod is decreased gradually. In addition, the radioactive substance decays gradually. Therefore, the level of the radioactivity in the pressure suppression chamber 6 is gradually decreased as shown in FIG. 7.
  • C represents the level of the radioactivity after elapse of time (t) from the moment of occurrence of the LOCA
  • Cio represents the level of the radioactivity of a radioactive substance (i) at a moment immediately after the occurrence of LOCA
  • ⁇ i represents the decay constant of the radioactive substance (i).
  • the accident judging device 28 can make a judgement as to whether the perforation of a fuel rod is taking place continuously, by determining the change of the level of the radioactivity after the occurrence of the perforation of fuel rod.
  • the display device 29 makes a display of "LOCA OCCURRED” and "DANGER OF FUEL ROD PERFORATION" in red.
  • the value 10 -2 ⁇ ci/cc used in the judgement at step M4 is derived from equations (2).
  • the accident judging device 28 provides an answer NO as a result of the judgement in each of the steps M1 to M3 and M5. Then, a step M6 is taken to make a judgement as to whether the condition of X+Y+Z ⁇ 10 5 ⁇ ci/cc is met.
  • An answer YES obtained as a result of the judgement in step M6 means that all of the fuel rods in the reactor core 2 have been broken and a part of these fuel rods have started to melt down. In this case, "LOCA OCCURRED”, "FUEL ROD PERFORATION” and "FUEL ROD MELT DOWN" are put on display in red.
  • an answer NO obtained as a result of the judgement in step M6 means that all of the fuel rods in the reactor core 2 started to melt down.
  • the display "FUEL ROD MELT DOWN" as obtained when the answer is YES is substituted by "ALL FUEL RODS MELT DOWN".
  • the monitoring system of the first embodiment it is possible to detect the occurrence of an LOCA, and to determine the state of fuel rods in the reactor core, i.e. the occurrence of perforation and melt down of fuel rods after the occurrence of the LOCA. It is also possible to know whether the perforation of the fuel rod is continuously spreading or not. Accordingly, it becomes possible to take suitable countermeasures without delay after the occurrence of LOCA.
  • the monitoring system of the first embodiment described heretofore has quite a simple construction. Namely, only one pipe is used to introduce the gas of the gas layer 8 to the iodine monitor 13 and the noble gas monitor 18.
  • the noble gas monitor 18 is disposed at the downstream side of the iodine monitor 13, it is possible to measure the concentrations of the radioactive iodine and the radioactive noble gas in the gas layer 8 at a high accuracy, with a simple construction. This is because the iodine is adsorbed by the iodine filter 15 of the iodine monitor 13 so that the gas flowing through the chamber 19 of the noble gas monitor 18 contains only the noble gas.
  • FIG. 9 shows another embodiment of the invention, in which the same reference numerals are used to denote the same parts as those in the first embodiment.
  • the pipe 30 having the iodine monitor 13 and the noble gas monitor 18 are connected at its both ends to the dry well 5 so that the levels of the radioactivities of radioactive iodine and radioactive noble gas in the dry well 5 are measured by the iodine monitor 13 and the noble gas monitor 18.
  • this embodiment offers the same advantages as the first embodiment described in connection with FIGS. 1 to 8.
  • FIG. 10 shows still another embodiment of the invention applied to another type of a reactor container of the boiling water reactor.
  • the container 31 is constituted by a dry well 32 and a pressure suppression chamber 33.
  • the pressure vessel 1 disposed in the dry well 32 is installed on a pedestal 34.
  • the dry well 32 and the pressure suppression chamber 33 are separated from each other by means of a diaphragm floor 35 secured to the pedestal 34.
  • a bent pipe 36 attached to the diaphragm floor 35 is immersed in the cooling water 7 in the pressure suppression chamber 33.
  • the pipe 11 connected to the gas layer 8 in the pressure suppression chamber 33 is provided with the noble gas monitor 18.
  • Another pipe 22 having the liquid radiation monitor 24 therein is immersed at its both ends in the cooling water within the pressure suppression chamber 33.
  • the levels of radioactivities measured by the noble gas monitor 18 and the liquid radiation monitor 24 are delivered to the accident judging device 28 for the judgement of the state of the reactor core.
  • the accuracy of the judgement is somewhat low as compared with those in the preceding embodiments, because the information concerning the radioactivity of iodine is not available, but the state of fuel rods in the reactor core can be determined with a satisfactorily high reliability.
  • the monitoring system as shown in FIG. 1 can be applied to the nuclear reactor core container 31 as shown in FIG. 10. Also, the monitoring system shown in FIG. 10 may be applied to the container shown in FIG. 1.
  • FIG. 11 there is shown a nuclear reactor core container 40 of the same type as that shown at FIG. 1 of the specification of U.S. Pat. No. 3,423,286.
  • This container 40 contains a coolant pump 37, a steam generator 38 and a reactor vessel 39.
  • An annular secondary shielding wall 41 is extended along the inner peripheral wall of the container 40.
  • the space between the inner peripheral surface of the container 40 and the secondary shielding wall 41 constitutes a condenser chamber 42 having a multiplicity of shelves 44 made of wire gauze and storing ice 43.
  • a water pool 45 is preserved at the bottom portion of the nuclear reactor container 40.
  • the iodine monitor 13 and the noble gas monitor 18 are installed in the pipe 11 which opens at its both ends in the space 46 within the container 10, while the liquid radiation monitor 24 is disposed in the pipe 22 which is communicated at its both ends with the water in the water pool 45.
  • the cooling water (coolant) in the reactor core vessel 39 is discharged in the state of steam into the space 46 within the container 40. That is the occurrence of LOCA.
  • the steam then flows into the condenser chamber 42 to come into contact with the ice 43 so as to be condensed by the latter.
  • the water produced as a result of the condensation flows into the water pool 45.
  • a pump 23 is started to introduce the water from the water pool 45 to the liquid radiation monitor 24 where the level of radioactivity (mainly radioactivity of radioactive iodine) is measured.
  • the blower 12 is driven continuously to permit the measurement of concentrations of the radioactive iodine and the radioactive noble gas in the gas staying within the space 46 by the iodine monitor 13 and the noble gas monitor 18.
  • the values measured by respective monitors are delivered to the accident judging device 28 which makes the judgement of the state of the reactor core in the same manner as the first embodiment shown in FIG. 1.
  • the pressure in the space 46 is measured continuously to sense the oecurence of LOCA from the change in the pressure.
  • the present invention makes it possible to accurately grasp the state of fuel rods in the reactor core after occurrence of LOCA, to permit the operator to take any necessary and suitable countermeasures to prevent the accident from being developed, thereby to contribute greatly to the safety of the nuclear reactor.

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  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Monitoring And Testing Of Nuclear Reactors (AREA)
US06/245,515 1980-03-19 1981-03-19 Monitoring system for monitoring state of nuclear reactor core Expired - Lifetime US4495142A (en)

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JP3534580A JPS56132594A (en) 1980-03-19 1980-03-19 Monitoring system for grasping core state at accident

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EP (1) EP0036332B1 (enrdf_load_stackoverflow)
JP (1) JPS56132594A (enrdf_load_stackoverflow)
DE (1) DE3172188D1 (enrdf_load_stackoverflow)

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US5019328A (en) * 1988-03-31 1991-05-28 Hitachi, Ltd. Natural circulation type boiling light-water reactor
US20040151274A1 (en) * 2003-01-31 2004-08-05 Kropaczek David Joseph Method of improving nuclear reactor performance
CN102054537A (zh) * 2009-11-11 2011-05-11 中科华核电技术研究院有限公司 一种核一级设备性能测试系统及方法
US9251920B2 (en) 2012-04-11 2016-02-02 Ge-Hitachi Nuclear Energy America Llc In-situ and external nuclear reactor severe accident temperature and water level probes
US10375901B2 (en) 2014-12-09 2019-08-13 Mtd Products Inc Blower/vacuum
CN112289468A (zh) * 2020-09-27 2021-01-29 西安交通大学 双面冷却燃料超高温氧化熔化行为测定实验装置及方法
WO2025020873A1 (zh) * 2023-07-25 2025-01-30 上海核工程研究设计院股份有限公司 一种核电站安全壳抽真空系统及方法

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JPS59126289A (ja) * 1983-01-10 1984-07-20 株式会社日立製作所 原子炉の破断検知装置
WO1992002021A1 (en) * 1989-07-14 1992-02-06 Kaplan H Charles Apparatus for the containment of nuclear meltdown debris
JPH0352595A (ja) * 1989-07-18 1991-03-06 Mini Pairo Denki:Kk ステッピングモータコントロール装置
SE514184C2 (sv) 1997-11-21 2001-01-22 Asea Atom Ab Förfarande och anordning för utvärdering av integriteten hos kärnbränslet i en nukleär anläggning
SE9904316L (sv) * 1999-11-29 2001-04-30 Westinghouse Atom Ab Förfarande för att driva en nukleär anläggning
CN111554425B (zh) * 2020-05-15 2022-02-11 中国核动力研究设计院 一种压水堆核电厂极小破口失水事故应对方法

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US5019328A (en) * 1988-03-31 1991-05-28 Hitachi, Ltd. Natural circulation type boiling light-water reactor
US20040151274A1 (en) * 2003-01-31 2004-08-05 Kropaczek David Joseph Method of improving nuclear reactor performance
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CN102054537A (zh) * 2009-11-11 2011-05-11 中科华核电技术研究院有限公司 一种核一级设备性能测试系统及方法
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JPS56132594A (en) 1981-10-16
DE3172188D1 (en) 1985-10-17
JPS6310799B2 (enrdf_load_stackoverflow) 1988-03-09
EP0036332A1 (en) 1981-09-23
EP0036332B1 (en) 1985-09-11

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